1. Field of the Invention
This invention relates to an electrical insulating oil composition which is prepared by bringing, into liquid-liquid contact with a polar solvent, a by-product oil fraction formed in the manufacture of ethylbenzene, ethyltoluene, cumene and the like, and furthermore it relates to electrical appliances impregnated with the above electrical insulating oil composition.
2. Description of the Prior Art
Heretofore, it is known that a heavy by-product oil is produced in the process to prepare ethylbenzene, ethyltoluene and the like by alkylating benzene, toluene and the like.
For example, it is disclosed in U.S. Pat. No. 4,111,825 to use, as an electrical insulating oil, a by-product oil in a benzene manufacture process to alkylate benzene with ethylene in the presence of, for example, an aluminum chloride catalyst, and similarly, U.S. Pat. No. 4,568,793 discloses that a by-product oil in an ethyltoluene manufacture process to alkylate toluene with ethylene is used as an electrical insulating oil.
On the other hand, oil-filled electrical appliances such as oil-filled capacitors recently have a noticeable tendency toward small size and lightweight, and in reply to this tendency, plastic materials for insulators and dielectrics have been developed and are now used together with or in place of conventional insulating papers.
Electrical insulating oils with which electrical appliances are impregnated also involve various problems in being used together with the above-mentioned plastic materials. That is, conventional electrical insulating oils, for example, refined mineral oils, polybutenes, alkylbenzenes and the like are not satisfactorily applied to plastic materials of polyolefins such as polypropylene, polymethylpentene and polyethylene which are used in the oil-filled electrical appliances. Some of these conventional electrical insulating oils dissolve or swell these plastic materials to deteriorate insulating power of the oil-filled electrical appliances on occasions.
None of the electrical insulating oils disclosed in the above-mentioned publications are preferable for the reason just described. For example, the above-mentioned publication, U.S. Pat. No. 4,568,793 disclosing the by-product oil of ethyltoluene refers to the excellent applicability of the oil to the plastic materials, but it is not always satisfactory and contains room for further improvement. This unsatisfactory effect would be due to some causes, and one of them is based on the by-product containing many components, chemical structurs of which are still unidentified. These unidentified components are inevitably contained in the by-product oil even when distillation is performed elaborately, and they cannot be identified. The inventors of the present application have found that certain components in the by-product oil deteriorate electrical properties of the by-product itself, for example, compatibility with the plastic materials.
With regard to the components in question, perfect identification of their structures is in fact impossible. Although the perfect removal of these components therefrom would not be impossible, but in such a case, extremely precise distillation is required, which is not economical.